The present invention is related to a method of localized liquid treatment of the surface of a substrate, like cleaning or etching. The invention is also related to an apparatus used to perform said treatment. Application of the invention is possible in a number of wet processing steps which are frequently used, e.g. in the fabrication of integrated circuits or liquid crystal displays.
In the fabrication of micro-electronic devices such as integrated circuits or liquid crystal displays, a substrate has to go through a number of fabrication steps, including wet etching, wet cleaning or rinsing.
In the documents U.S. Pat. No. 5,271,774 and Japanese Patent JP-A-07211686, methods are described to remove a liquid from the surface of a substrate by applying a gaseous substance to the substrate, which, when mixed with the liquid, reduces the surface tension of the liquid, so that it can be easily removed from the surface by a centrifugal force, i.e. by subjecting the substrate to a rotary movement. However, these methods are only applicable to the substrate a whole, and cannot be used for local treatment of the substrate. Document EP-A-817246 is describing an apparatus and method for wet cleaning or etching of flat substrate surfaces, whereby a substrate is moved through a stationary amount of liquid. This method is also related to a treatment of the substrate as a whole, not of a local zone of said substrate.
During some processing steps, an annular edge area of the substrate is treated, for example for the removal of certain layers, like a resist or a metal film (e.g. Cu). Sometimes, it is only the outer rim of the substrate which is treated, while the top and bottom surfaces of the substrate must remain untouched.
Techniques exist whereby a beam of liquid is directed to the edge area or the rim of a rotating substrate in order to perform these process steps. However these existing techniques offer a poor protection of the substrate surface against the cleaning liquid. It would therefore be advantageous to find a way of protecting the substrate surface while treating said annular edge area or its outer rim with a liquid. Another disadvantage of existing techniques is that the rotational speed of the substrate during processing must be relatively high, which is particularly problematic for large substrates.
Some processing steps require the removal of larger sized features from the substrate surface, e.g. for revealing underlying zero markers, which are used for the accurate lateral positioning during processing, e.g., during photographic exposure. Although the definition of the zero markers themselves requires high accuracy, the accuracy requirements of the window for removing a layer on top of the zero markers can be fairly relaxed. So far in the state of the art, the use of a photo resist step is mostly used to accomplish these areas. By using a photo resist step, a patterned protective resist layer is obtained on the substrate surface. The pattern is such that the areas to be etched are not covered with resist. After this, the substrate is etched and the photo resist layer is removed. This is however an expensive and time-consuming effort.
An alternative way of producing such larger sized areas which are free of film, consists of a local shielding by shielding plates during film deposition. However, this technique leads to an increased risk of particle contamination and scratch formation on the substrate. Furthermore, this shielding technique is not generally applicable. It requires compatibility of the shielding plates with the deposition process of interest. To produce these larger sized features, it would therefore be advantageous to find a method that allows less accuracy but lower cost and higher processing speed, without creating any particle contamination.
Document JP-A-11166882 describes a pre-concentration or collection technique, used in contamination measurements for semi-conductors. It is a technique, whereby a droplet is moved over the substrate surface, in order to collect contaminants and subsequently analyze their concentrations. Currently, this technique is mainly used on silicon surfaces, by rendering the surface hydrophobic by way of an HF-treatment. This way, the water-based droplet is contained. The technique is however not confined to silicon surfaces. In some cases, it has been observed that the contact angle between the droplet and the substrate surface is insufficient. Furthermore, it would be advantageous to find a method whereby, in the case of silicon surfaces, the extra processing step of providing an HF-treatment would become unnecessary.
Document U.S. Pat. No. 5,492,566 describes a way of holding a substrate to a flat surface by way of the Bernoulli effect. By supplying a gas at a high speed between said substrate and said surface through an annular nozzle, a pressure drop will result, under said substrate, thus holding said substrate to said surface. Substrates held in this way can be subjected to various wet treatment steps, like cleaning or etching. However, a danger exists of liquid attaching itself to the rim or the backside of the substrate.
The present invention relates to a method of dispensing liquid on a part of a substrate for processing of the substrate, e.g. for cleaning or etching purposes, while another part of said substrate is prevented from contacting said liquid, said method comprising the steps of:
supplying a liquid on a part of said substrate; and
simultaneously with said step of supplying a liquid, supplying a gaseous tensio-active substance to a surface, said gaseous substance being at least partially miscible with said liquid and when mixed with said liquid yielding a mixture having a surface tension lower than that of said liquid.
A first embodiment of the invention is a method wherein said substrate is circular shaped,
wherein the step of supplying a liquid on a part of said substrate includes supplying at least one stream of a liquid so that said stream hits a flat surface of said substrate in an area of said surface, said area being adjacent to an outer rim of said substrate,
wherein the step of supplying a gaseous tensio-active substance to said surface includes supplying at least one stream of a gaseous tensio-active substance to the flat surface of said substrate so that said stream hits said surface in an area which is adjacent to the area hit by said liquid stream, and closer to the center of rotation, and
further comprising the step of:
rotating the circular shaped substrate about an axis of rotation, preferably in a horizontal plane, the axis being perpendicular to the substrate surface and through a center of gravity said substrate.
An additional stream of liquid may be supplied to the opposite surface of said substrate, in order to treat the whole of said opposite surface.
According to another embodiment of the invention, a stream of liquid may be directed at the outer rim of the substrate, while the flat surfaces are protected from said liquid by a stream of a gaseous tensio-active substance.
Another embodiment of the invention is a method wherein the substrate is circular shaped and has two sides, a first side consisting of an annular edge area and a central area,
the method further comprising the step of holding the circular shaped substrate,
wherein the step of supplying a liquid on a part of said substrate includes supplying a stream of liquid to the entire annular edge area of the first side of the substrate, and
wherein the step of supplying a stream of a gaseous tensio-active substance includes supplying a stream of a gaseous tensio-active substance to the central area of the surface.
In this method, the substrate may be subjected to a rotational movement, the axis of rotation being perpendicular to the substrate surface and comprising the center of said substrate.
An additional stream of liquid may be supplied to a surface which is opposite to a surface of which the annular edge area is treated, in order to treat the whole of said opposite surface.
Another embodiment of the present invention is a method wherein a is circular shaped, wherein the step of supplying a gaseous tensio-active substance to said surface includes supplying streams of a gaseous tensio-active substance to border areas between said amount of liquid and said flat surfaces, and
further comprising the steps of:
holding the circular shaped substrate, and
providing a means of bringing an annular edge area of both flat surfaces of said substrate, and the outer rim of said substrate into contact with an amount of liquid.
In this method, the substrate may be subjected to a rotational movement, the axis of rotation being perpendicular to the substrate surface and comprising the center of said substrate.
Another embodiment of the present invention is a method, wherein the substrate has two sides, a first side and a second side,
further comprising the step of placing the second side of the substrate on a flat, rotating surface, said rotating surface containing an annular channel, so that said second side of said substrate is covering said channel,
wherein said step of supplying a gaseous tensio-active substance includes supplying a stream of gaseous tensio-active substance through said annular channel and in the direction of said substrate, so that said substrate is held on said rotating surface by a Bernoulli effect, and
wherein said step of supplying a liquid on a part of said substrate includes supplying a stream of the liquid on the first side of said substrate.
Another embodiment of the present invention is a method, wherein the substrate has a first side and a second side,
wherein the step of supplying a liquid on a part of said substrate includes supplying, through a first channel, a continuous stream of liquid to a part of the first side of the substrate which is preferably horizontally placed,
further comprising the step of draining said stream of liquid from said first side through a second channel, the second channel being concentrically placed around the first channel,
and wherein the step of supplying a gaseous tensio-active substance includes supplying to said first side a stream of a gaseous tensio-active substance around said second channel, to prevent remainder liquid from making contact with the first side of the substrate which is not contained within the second channel. In this embodiment, the gaseous tensio-active substance may be drained from the substrate surface through an additional channel.
Another embodiment of the present invention is a method, wherein the step of supplying a liquid on a part of said substrate includes bringing an amount of liquid into contact with a part of a flat surface which is preferably horizontally placed, and
wherein the step of supplying a gaseous tensio-active substance to said surface includes supplying to said surface a stream of gaseous tensio-active substance around said amount of liquid, thereby preventing said liquid from making contact with the rest of said surface. In this embodiment, the gaseous tensio-active substance may be drained from the substrate surface through an additional channel.
The present invention is also related to an apparatus for subjecting a substrate to a localized liquid treatment for cleaning or etching of the substrate, said apparatus comprising means for holding said substrate, a first supply system adapted to supply a liquid on a first part of the surface of said substrate, and a second supply system adapted to supply a gaseous substance to a second part of said substrate, the second part of the substrate adjacent to the first part which is treated by said liquid.
In such an apparatus, a means may be provided for rotating said substrate around an axis which is perpendicular to said substrate and which comprises the center of said substrate.
According to one embodiment, an apparatus is proposed for treating an annular edge area of at least one flat surface of a circular shaped, preferably horizontally placed substrate, comprising at least one fixed pair of nozzles, a nozzle being defined as an apparatus able to supply a contiguous stream of liquid. Of this pair, one nozzle is used to supply a stream of liquid on said annular edge area, while the other is used to dispense a gaseous tensio-active substance on an area of said flat surface adjacent to said annular edge area, and closer to the center of said substrate.
Said pair of nozzles may be positionable on any location along a fixed radius of said substrate. A nozzle may be added on one of the flat surfaces of said substrate which is opposite to a surface of which the edge area is treated, said nozzle being used to dispense a stream of liquid on the whole of said opposite surface.
According to another embodiment, an apparatus is provided for treating an annular edge area of a flat surface of a circular shaped substrate, the apparatus having a first supply system and a second supply system,
wherein the substrate has a geometric center, an axis which is perpendicular to said substrate at the geometric center of said substrate, a central part around the axis of the substrate and an annular edge,
wherein said first supply system includes a first annular channel adapted to supply the liquid to the entire annular edge area of the surface of said substrate,
wherein said second supply system includes a central channel adapted to supply a gaseous substance to the central part of said substrate, the central channel being coaxial with the axis of the substrate, and
wherein said second supply system further includes a second annular channel placed concentrically with respect to the first channel and closer to the geometric center of said substrate, said second channel adapted to guide the gaseous substance coming from the central part of said substrate, in order to prevent said liquid from touching said central part.
Said apparatus may rotate around an axis which is perpendicular to said substrate and which comprises the center of said substrate. A nozzle may be added on one of the flat surfaces of said substrate which is opposite to a surface of which the edge area is treated, said nozzle being used to dispense a stream of liquid on the whole of said opposite surface.
A sealing device may be added between said substrate and the outer wall of said second annular channel.
According to another embodiment, an apparatus is proposed for treating an annular edge area of both flat surfaces and the outer rim of a circular shaped substrate, placed preferably in a horizontal plane, comprising:
means for holding said substrate,
a first supply system adapted to supply a liquid on a first part of the surface of said substrate,
a second supply system adapted to supply a gaseous substance to a second part of said substrate,
a container filled with an amount of treatment liquid so that a pressure is maintained above the surface of said amount of treatment liquid, said pressure being less than or equal to an ambient pressure, said container having a narrow gap in one side, into which said circular substrate is partially inserted, so that at least a portion of said annular edge and said outer rim of said substrate is immersed in said liquid, and
at least one pair of nozzles, one nozzle of said pair on each side of said substrate, directing a stream of a gaseous substance at a border area between said container and said substrate.
Said apparatus may rotate around an axis which is perpendicular to said substrate and which comprises the center of said substrate.
According to another embodiment, an apparatus is proposed for treating a local zone of a preferably horizontally placed substrate, said apparatus comprising
a first supply system including a central channel used to supply a stream of liquid to the surface of said substrate and a second channel, concentrically surrounding the first channel, and draining said stream of liquid from the surface of said substrate; and
a second supply system including a third channel, concentrically surrounding the second channel and used to supply a stream of a tensio-active substance to the substrate surface.
According to the same embodiment, a fourth channel may be concentrically placed with respect to said third channel, said fourth channel being used to drain said gaseous tensio-active substance from the substrate surface.
A sealing device may be added between said substrate and the outer wall of said second channel. In case of a fourth channel, an additional sealing device may be placed between said substrate and the outer wall of the apparatus.
According to another embodiment, an apparatus is proposed for treating a local zone or for collecting impurities from the surface of a preferably horizontally placed substrate, said apparatus comprising:
a first supply system including a central channel, the central channel containing an amount of a liquid such that said liquid is in contact with the surface of said substrate, and that a pressure is maintained above a surface of said amount of liquid, said pressure being less than or equal to an ambient pressure on the substrate surface, and
a second supply system including a second channel, the second channel concentrically surrounding the central channel, and supplying a stream of a gaseous tensio-active substance on the surface of said substrate.
According to the same embodiment, a third channel may be placed concentrically with respect to said second channel, said third channel being used to drain said gaseous tensio-active substance from the substrate surface.
A sealing device may be added between said substrate and the outer wall of said central channel. In case of a third channel, an additional sealing device may be placed between the substrate and the outer wall of the apparatus.
An object of the present invention is to provide a method and apparatus to perform a liquid treatment of a part of a substrate, such as a cleaning or etching step, while another part of said substrate is protected from said liquid by the use of a gaseous substance.